The present invention is directed to electrical switch arrays, and especially to electrical keyswitch arrays, or keypads, of the sort used for portable devices, such as portable telephones, wireless telephones, personal digital assistant (PDA) devices and similar devices.
Often during use of such products a condition occurs where one or more keys is stuck or otherwise held in an actuated position. For example, a wireless phone in the bottom of a user's purse or in a user's pocket may have one or more of the keys in its keypad array inadvertently pressed and held down (i.e., in an actuated position) for a long period of time. Depending upon the circuit design and implementation of the keypad interface such a holding down of a keyswitch can draw power and cause excess current to flow. Excess current flow can prematurely drain the batteries in battery-operated products such as wireless phones, PDA devices and similar products.
Previous solutions to this problem of inadvertent current drain have involved having a microprocessor or similar computing device “wake up” the system from a “sleep” mode. The sleep mode is a mode in which only minimal activity is carried out by an apparatus in order that only minimal power is required so that minimal current drain occurs. The device is “awakened” periodically every 10-20 μsec (microseconds) and polling or other examination of the keypad is carried out to determine whether a key is being held down. If a key is determined to be held down, the device remains awake and processes the information imparted by the holding down of the key. The problem with such prior art solutions is that the required periodic “awakening” and the repeated polling consume a certain amount of power and therefore cause current drain that shortens battery life.
There is a need for an apparatus and method for controlling an electrical switch array that requires less power to operate than is required by presently available control apparatuses and methods.